Coles (STC) Commentator's Lip Mic

[paulears]

I've got an old lip mic - it's one of the first ones branded with the Coles name. It's always been fine, but I decided to dismantle it to give it a clean, so removed all the filters and filter holders, and took the front and back grills off and blew them out. I didn't remove the internal pinky/gold mesh from the mouth side - and the inside was actually spotless anyway. After re-assembly, the tone was much thinner. Oddly, if you talk into the rear or the side, my voices sounds full, but the mouth side is definitely 'odd'. Removing the grills again, and speaking into the proper side, the tone is fine - so I've done something to the grill assembly. I wonder if the two thin pieces of tiny perforations that are sandwiched in the oval frame need to be aligned in some special way - I did pull these apart, and it occurs to me that maybe the 'hole' alignment was factory fixed, and I have destroyed it, effectively blocking the audio path?

 

Has anyone any ideas on what I have done - it's useless at the moment - and the grill is the only thing I can think of?

[peza2010]

from your description, I can imagine that the two grilles are misaligned, so between the top and bottom grille the mesh doesnt actualy allow a clear path through?

[kerry davies]

Have a read of This PDF

 

If nothing else it gives an email address to seek advice but I reckon your diagnosis is correct. The air flow through the mic appears to have been "diverted" (rather than "blocked") and according to the PDF that will affect the bottom end predominantly. It might be that you have inverted one of the grilles or placed one "backwards", though that is just guessing.

 

The rear grilles "should" be identical in alignment and if you have that side working OK it might be an idea to remove them again and note how they are set up???

[grizzly]

Unfortunately, the PDF linked above is for a Coles 4038 studio mic, rather than the 4104 (or possibly 4115) lip mic, so the internal construction will probably be quite different.

[kerry davies]

Agreed Grizz, though the principles should be the same and the mention of flow affecting predominantly the bottom end correlates to what Paul has diagnosed. The Coles website has actually cut'n'pasted bits of the 4038 tech spec into the spec for the 4115 so I would assume they are pretty closely allied.

 

I have a vague memory of the grilles being dot-marked for alignment but that was probably done by in-house technical staff and it is nearly 20 years since I handled a 4104. You are possibly the BR expert on these in comparison to most of us, could you have a look at one sometime?

[grizzly]

I will try to remember to have a butchers, next time I'm in the vicinity of one of our spares.

[paulears]

The front and back removable hemispheres appear to be identical - the only difference is that the front centre fixing screw also serves to anchor the pair of micro-mesh filters. There is an open frame, and then the mesh is sandwiched between the frame and a front screw on plate that clamps the mesh. This came out as one, but was on investigation two, layered together. I gently peeled them apart and blew them out. The mesh is so fine that it's difficult to blow air from your mouth through it. Holding it up to the light reveals little light coming through either. I simply put the two layers back together, put the screws back in through the original holes and did them up. There's a very similar mesh on the top, designed to stop your nose wind from getting to the top part of the housing. To complete assembly, there's another guard that snaps onto the lip bar, and I think it is used to sandwhich a piece of lint type material for hygiene reasons.

 

Perhaps I should try removing one of the pieces of mesh and seeing if the bottom end returns - although there is a possibility that the last person who used it could have used it without the spit guard, and this has condensed on the mesh and set - blocking the holes?

 

If anyone does have one they could compare, I'd really appreciate it.

 

Paul

[Rob_Beech]

I have one in hire stock, I will look how things appear to be placed, I've never taken one apart before though. What could possibly go wrong?

[paulears]

Rob - just in case you wreck yours - there are four screw heads visible on the frame that has the front sliver mesh plate. 3 have threads into the sub frame and one on mine has a nut on the back. this is the bit I may have wrecked. If yours is a layer of two, stuck together - then don't prise them apart. I assumed (probably the mistake) that they were stuck together by spit - maybe they weren't? So if yours are a stuck together layer, don't go any further, because that could be the problem. Any comments on yours would help. With this grill off, then there is considerably more bass response - and it sounds quite good, but with it on - it's now horrible.

Paul

[paulears]

I've given up. I even emailed Coles, and got no response at all. A bit sad really. I'll give it another go when I get more time.